Medium and heavy-duty trucks and tractors often have a suspension system installed between the truck frame and the driver's cab which reduces shock and vibration transmitted from the frame to the cab and thereby enhances driver comfort. As shown in FIGS. 1, 2 and 3 of the drawings, a typical prior art suspension system, generally designated 10, is adapted to interconnect a truck cab 12 and an associated truck frame 14. The frame 14 typically includes rails 16, 18 joined by a transverse frame element 20. The forward portion 22 of the cab 12 is mounted on the frame 14 by bushings 24, 26. Bushings 24, 26 provide a flexible attachment for the front 22, while controlling relative fore and aft cab movement, as well as restricting lateral movement of the cab 12 relative to the frame 14.
The rear 28 of the cab 12 is attached to the frame 14 by a system that includes standard shock absorbers 30, 32, a panhard rod or transverse link 34, air springs 36, 38, and a height sensor or air control valve 40. The shock absorbers 30, 32 dampen vertical motion between the rear 28 of the cab 12 and the frame 14, and the panhard rod 34 restricts relative lateral motion between the cab and the frame. The air springs 36, 38 support the rear 28 of the cab 12 above the frame 14 and are selectively pressurized by the air control valve 40, which is connected to a source of pressurized air (not shown), in order to maintain the rear 28 of the cab 12 a predetermined distance above the frame 14 in response to varying loads in the cab.
A disadvantage with such prior art systems as the suspension system 10 shown in FIGS. 1–3 is that such systems are overly complex, relatively expensive and occupy a relatively large amount of space beneath the cab and between the rails of the associated frame. Accordingly, there is a need for a suspension system for a truck cab that minimizes the components required to perform the suspension and shock absorbing function, provides lateral support and shock damping features, and at the same time minimizes the space required in the area between the cab and frame rates. There is also a need for a cab suspension system that controls cab ride height and provides an improved ride.